Runtime error with PlayCanvas due to mismatch between native WebXR implementation and emulation runtime

[mrxz]

When using the immersive-web-emulator on a PlayCanvas application in Chrome, the following exception occurs when starting the XR session:

Immersive VR failed to start: this._manager.session.getTrackedImageScores is not a function

The cause for this does lie within PlayCanvas, as it performs feature detection for the WebXR Marker Tracking Module based on the existence of the XRImageTrackingResult class (see playcanvas/engine#5365). While I do think PlayCanvas could, and perhaps should, rely on enabledFeatures instead, it's backwards to change an engine based on an emulator.

This does highlight a potential source of issues when the native WebXR implementation of the browser supports a different feature set than the emulation runtime. Ideally the native implementation is completely overridden when the emulation runtime is loaded, ensuring a consistent environment. Overriding/deleting classes belonging to unsupported WebXR modules/APIs could be an option, but might become tricky when considering name changes and experimental/draft implementations.

[mrxz]

Turns out that Chrome does not expose XRImageTrackingResult on desktop clients by default, but it's behind the #enable-experimental-web-platform-features flag, which I have enabled. So the odds of people running into this issue are probably very slim.

[msub2]

Also ran into this today, I believe the flag causing it is actually #webxr-incubations, as disabling that stopped the error for me.